Operational control of wellsite pumping unit with displacement determination

ABSTRACT

A well pumping system can include an actuator that reciprocably displaces a rod string, a flowmeter that measures flow of a fluid between a power source and the actuator, and a control system that modifies reciprocal displacement of the rod string by the actuator, in response to an output of the flowmeter. A well pumping method can include reciprocably displacing a rod string, continuously determining a velocity profile of the rod string, and modifying the velocity profile while the rod string reciprocably displaces, in response to an output of a flowmeter. Another well pumping method can include reciprocably displacing a rod string with an actuator, continuously determining displacement in response to an output of a flowmeter, and modifying reciprocating displacement of the rod string by the actuator, in response to the output of the flowmeter.

BACKGROUND

This disclosure relates generally to equipment utilized and operationsperformed in conjunction with a subterranean well and, in one exampledescribed below, more particularly provides a well pumping system andassociated method.

Reservoir fluids can sometimes flow to the earth's surface when a wellhas been completed. However, with some wells, reservoir pressure may beinsufficient (at the time of well completion or thereafter) to lift thefluids (in particular, liquids) to the surface. In those circumstances,technology known as “artificial lift” can be employed to bring thefluids to or near the surface (such as a subsea production facility orpipeline, a floating rig, etc.).

Various types of artificial lift technology are known to those skilledin the art. In one type of artificial lift, a downhole pump is operatedby reciprocating a string of “sucker” rods deployed in a well. Anapparatus (such as, a walking beam-type pump jack or a hydraulicactuator) located at the surface can be used to reciprocate the rodstring.

Therefore, it will be readily appreciated that improvements arecontinually needed in the arts of constructing and operating artificiallift systems. Such improvements may be useful for lifting oil, water,gas condensate or other liquids from wells, may be useful with varioustypes of wells (such as, gas production wells, oil production wells,water or steam flooded oil wells, geothermal wells, etc.), and may beuseful for any other application where reciprocating motion is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representative partially cross-sectional view of an exampleof a well pumping system and associated method which can embodyprinciples of this disclosure.

FIGS. 2-5 are representative views of actuator examples and continuousposition sensor examples.

FIGS. 6-9 are representative graphs of example velocity profiles.

FIGS. 10 & 11 are representative flowcharts for techniques ofcontrolling operation of the well pumping system.

FIG. 12 is a representative example graph of position and energy inputversus time, with modifications thereof.

FIGS. 13 & 14 are representative views of further actuator examples.

DETAILED DESCRIPTION

Representatively illustrated in FIG. 1 is a well pumping system 10 andassociated method for use with a subterranean well, which system andmethod can embody principles of this disclosure. However, it should beclearly understood that the well pumping system 10 and method are merelyone example of an application of the principles of this disclosure inpractice, and a wide variety of other examples are possible. Therefore,the scope of this disclosure is not limited at all to the details of thesystem 10 and method as described herein or depicted in the drawings.

In the FIG. 1 example, a power source 12 is used to supply energy to anactuator 14 mounted on a wellhead 16. In response, the actuator 14reciprocates a rod string 18 extending into the well, thereby operatinga downhole pump 20.

The rod string 18 may be made up of individual sucker rods connected toeach other, although other types of rods or tubes may be used, the rodstring 18 may be continuous or segmented, a material of the rod string18 may comprise steel, composites or other materials, and elements otherthan rods may be included in the string. Thus, the scope of thisdisclosure is not limited to use of any particular type of rod string,or to use of a rod string at all. It is only necessary for purposes ofthis disclosure to communicate reciprocating motion from the actuator 14to the downhole pump 20, and it is therefore within the scope of thisdisclosure to use any structure capable of such transmission.

The downhole pump 20 is depicted in FIG. 1 as being of the type having astationary or “standing” valve 22 and a reciprocating or “traveling”valve 24. The traveling valve 24 is connected to, and reciprocates with,the rod string 18, so that fluid 26 is pumped from a wellbore 28 into aproduction tubing string 30. However, it should be clearly understoodthat the downhole pump 20 is merely one example of a wide variety ofdifferent types of pumps that may be used with the well pumping system10 and method of FIG. 1, and so the scope of this disclosure is notlimited to any of the details of the downhole pump described herein ordepicted in the drawings.

The wellbore 28 is depicted in FIG. 1 as being generally vertical, andas being lined with casing 32 and cement 34. In other examples, asection of the wellbore 28 in which the pump 20 is disposed may begenerally horizontal or otherwise inclined at any angle relative tovertical, and the wellbore section may not be cased or may not becemented. Thus, the scope of this disclosure is not limited to use ofthe well pumping system 10 and method with any particular wellboreconfiguration.

In the FIG. 1 example, the fluid 26 originates from an earth formation36 penetrated by the wellbore 28. The fluid 26 flows into the wellbore28 via perforations 38 extending through the casing 32 and cement 34.The fluid 26 can be a liquid, such as oil, gas condensate, water, etc.However, the scope of this disclosure is not limited to use of the wellpumping system 10 and method with any particular type of fluid, or toany particular origin of the fluid.

As depicted in FIG. 1, the casing 32 and the production tubing string 30extend upward to the wellhead 16 at or near the earth's surface 40 (suchas, at a land-based wellsite, a subsea production facility, a floatingrig, etc.). The production tubing string 30 can be hung off in thewellhead 16, for example, using a tubing hanger (not shown). Althoughonly a single string of the casing 32 is illustrated in FIG. 1 forclarity, in practice multiple casing strings and optionally one or moreliner strings (a liner string being a pipe that extends from a selecteddepth in the wellbore 28 to a shallower depth, typically sealingly “hungoff” inside another pipe or casing) may be installed in the well.

In the FIG. 1 example, a rod blowout preventer stack 42 and a stuffingbox 44 are connected between the actuator 14 and the wellhead 16. Therod blowout preventer stack 42 includes various types of blowoutpreventers (BOP's) configured for use with the rod string 18. Forexample, one blowout preventer can prevent flow through the blowoutpreventer stack 42 when the rod string 18 is not present therein, andanother blowout preventer can prevent flow through the blowout preventerstack 42 when the rod string 18 is present therein. However, the scopeof this disclosure is not limited to use of any particular type orconfiguration of blowout preventer stack with the well pumping system 10and method of FIG. 1.

The stuffing box 44 includes an annular seal (not visible in FIG. 1)about an upper end of the rod string 18. A reciprocating rod member 50of the actuator 14 connects to the rod string 18 above the annular seal,although in other examples a connection between the rod member 50 andthe rod string 18 may be otherwise positioned.

The power source 12 may be connected directly to the actuator 14, or itmay be positioned remotely from the actuator 14 and connected with, forexample, suitable electrical cables, mechanical linkages, hydraulichoses or pipes. Operation of the power source 12 is controlled by acontrol system 46.

The control system 46 may allow for manual or automatic operation of theactuator 14 via the power source 12, based on operator inputs andmeasurements taken by various sensors. The control system 46 may beseparate from, or incorporated into, the actuator 14 or the power source12. In one example, at least part of the control system 46 could beremotely located or web-based, with two-way communication between theactuator 14, the power source 12 and the control system 46 being via,for example, satellite, wireless or wired transmission.

The control system 46 can include various components, such as aprogrammable controller, input devices (e.g., a keyboard, a touchpad, adata port, etc.), output devices (e.g., a monitor, a printer, arecorder, a data port, indicator lights, alert or alarm devices, etc.),a processor, software (e.g., an automation program, customized programsor routines, etc.) or any other components suitable for use incontrolling operation of the actuator 14 and the power source 12. Thescope of this disclosure is not limited to any particular type orconfiguration of a control system.

In operation of the well pumping system 10 of FIG. 1, the control system46 causes the power source 12 to increase energy input to the actuator14, in order to raise the rod string 18. Conversely, the energy input tothe actuator 14 is reduced or removed, in order to allow the rod string18 to descend. Thus, by alternately increasing and decreasing energyinput to the actuator 14, the rod string 18 is reciprocated, thedownhole pump 20 is actuated and the fluid 26 is pumped out of the well.

Note that, when energy input to the actuator 14 is decreased to allowthe rod string 18 to displace downward (as viewed in FIG. 1), the energyinput may not be decreased to zero. Instead, a “balance” energy levelmay be maintained in the actuator 14 to nominally offset a load due tothe rod string 18 being suspended in the well (e.g., a weight of the rodstring, taking account of buoyancy, inclination of the wellbore 28,friction, well pressure, etc.).

In this manner, the power source 12 is not required to increase energyinput to the actuator 14 from zero to that necessary to displace the rodstring 18 upwardly (along with the displaced fluid 26), and then reducethe energy input back to zero, for each reciprocation of the rod string18. Instead, the power source 12 only has to increase energy input tothe actuator 14 sufficiently greater than the balance energy level todisplace the rod string 18 to its upper stroke extent, and then reducethe energy input to the actuator 14 back to the balance energy level toallow the rod string 18 to displace back to its lower stroke extent.

Note that it is not necessary for the balance energy level in theactuator 14 to exactly offset the load exerted by the rod string 18. Insome examples, it may be advantageous for the balance energy level to besomewhat less than that needed to offset the load exerted by the rodstring 18. In addition, it can be advantageous in some examples for thebalance energy level to change over time. Thus, the scope of thisdisclosure is not limited to use of any particular or fixed balanceenergy level, or to any particular relationship between the balanceenergy level, any other force or energy level and/or time.

A reciprocation speed of the rod string 18 will affect a flow rate ofthe fluid 26. Generally speaking, the faster the reciprocation speed ata given length of stroke of the rod string 18, the greater the flow rateof the fluid 26 from the well (to a point).

It can be advantageous to control the reciprocation speed, instead ofreciprocating the rod string 18 as fast as possible. For example, afluid interface 48 in the wellbore 28 can be affected by the flow rateof the fluid 26 from the well.

The fluid interface 48 could be an interface between oil and water, gasand water, gas and gas condensate, gas and oil, steam and water, or anyother fluids or combination of fluids.

If the flow rate is too great, the fluid interface 48 may descend in thewellbore 28, so that eventually the pump 20 will no longer be able topump the fluid 26 (a condition known to those skilled in the art as“pump-off”). On the other hand, it is typically desirable for the flowrate of the fluid 26 to be at a maximum level that does not result inpump-off. In addition, a desired flow rate of the fluid 26 may changeover time (for example, due to depletion of a reservoir, changed offsetwell conditions, water or steam flooding characteristics, etc.).

A “gas-locked” downhole pump 20 can result from a pump-off condition,whereby gas is received into the downhole pump 20. The gas isalternately expanded and compressed in the downhole pump 20 as thetraveling valve 24 reciprocates, but the fluid 26 cannot flow into thedownhole pump 20, due to the gas therein.

In the FIG. 1 well pumping system 10 and method, the control system 46can automatically control operation of the actuator 14 via the powersource 12 to regulate the reciprocation speed, so that pump-off isavoided, while achieving any of various desirable objectives. Thoseobjectives may include maximum flow rate of the fluid 26, optimized rateof electrical power consumption, reduction of peak electrical loading,etc. However, it should be clearly understood that the scope of thisdisclosure is not limited to pursuing or achieving any particularobjective or combination of objectives via automatic reciprocation speedregulation by the control system 46.

As mentioned above, the power source 12 is used to variably supplyenergy to the actuator 14, so that the rod string 18 is displacedalternately to its upper and lower stroke extents. These extents do notnecessarily correspond to maximum possible upper and lower displacementlimits of the rod string 18 or the pump 20.

For example, it is typically undesirable for a valve rod bushing 25above the traveling valve 24 to impact a valve rod guide 23 above thestanding valve 22 when the rod string 18 displaces downward (a conditionknown to those skilled in the art as “pump-pound”). Thus, it ispreferred that the rod string 18 be displaced downward only until thevalve rod bushing 25 is near its maximum possible lower displacementlimit, so that it does not impact the valve rod guide 23.

On the other hand, the longer the stroke distance (without impact), thegreater the productivity and efficiency of the pumping operation (withinpractical limits), and the greater the compression of fluid between thestanding and traveling valves 22, 24 (e.g., to avoid gas-lock). Inaddition, a desired stroke of the rod string 18 may change over time(for example, due to gradual lengthening of the rod string 18 as aresult of lowering of a liquid level (such as at fluid interface 48) inthe well, etc.).

In the FIG. 1 well pumping system 10 and method, the control system 46can automatically control operation of the power source 12 to regulatethe upper and lower stroke extents of the rod string 18, so thatpump-pound is avoided, while achieving any of various desirableobjectives. Those objectives may include maximizing rod string 18 strokelength, maximizing production, minimizing electrical power consumptionrate, minimizing peak electrical loading, etc. However, it should beclearly understood that the scope of this disclosure is not limited topursuing or achieving any particular objective or combination ofobjectives via automatic stroke extent regulation by the control system46.

In the FIG. 1 example, the system 10 includes a continuous positionsensor 52 in communication with the control system 46. The continuousposition sensor 52 is capable of continuously detecting a position of areciprocating member of the actuator 14 (such as the rod member 50 oranother member).

An output of the continuous position sensor 52 can be useful to achievea variety of objectives, such as, controlling stroke distance, speed andextents to maximize production and efficiency, minimize electrical powerconsumption and/or peak electrical loading, maximize useful life of therod string 18, etc.

However, the scope of this disclosure is not limited to pursuing orachieving any particular objective or combination of objectives via useof a continuous position sensor.

As used herein, the term “continuous” is used to refer to asubstantially uninterrupted sensing of position by the sensor 52. Forexample, when used to continuously detect the position of the rod member50, the sensor 52 can detect the member's position during all portionsof its reciprocating motion, and not just at certain discrete points(such as, at the upper and lower stroke extents). However, a continuousposition sensor may have a particular resolution (e.g., 0.001-0.1 mm) atwhich it can detect the position of a member. Accordingly, the term“continuous” does not require an infinitely small resolution.

Using the continuous position sensor 52, the control system 46 can beprovided with an accurate measurement of an actuator 14 member positionat any point in the member's reciprocation, thereby dispensing with anyneed to perform calculations based on discrete detections of position.It will be appreciated by those skilled in the art that actualcontinuous position detection can be more precise than such calculationsof position, since various factors (including known and unknown factors,such as, temperature, fluid compressibility, fluid leakage, etc.) canaffect the calculations. However, such calculations of position may beused in keeping with the principles of this disclosure, either inconjunction with, or instead of, continuous position measurements.

By continuously sensing the position of a member of the actuator 14 ator near a top of the rod string 18, characteristics of the rod string'sreciprocating displacement are communicated to the control system 46 ateach point in the rod string's reciprocating displacement. The controlsystem 46 can, thus, determine whether the rod string's 18 position,speed and acceleration correspond to desired preselected values.

If there is a discrepancy between the desired preselected values and therod string's reciprocating displacement as detected by the sensor 52,the control system 46 can change how energy is supplied to the actuator14 by the power source 12, so that the reciprocating displacement willconform to the desired preselected values. For example, the controlsystem 46 may change a level, timing, frequency, duration, etc., of theenergy input to the actuator 14, in order to change the rod string'supper or lower stroke extent, or velocity or acceleration at any pointin the rod string's reciprocating displacement.

Note that the desired preselected values may change over time. Asmentioned above, it may be desirable to change the upper or lower strokeextent, or the pumping rate, during the pumping operation, for example,due to the level of the fluid interface 48 changing, reservoir depletionover time, detection of a pump-off, pump-pound or gas-lock condition,etc.

Referring additionally now to FIGS. 2-5, examples of different actuators14 that may be used with the system 10 and method are representativelyillustrated. These examples are not limiting of the scope of thisdisclosure, but are instead provided to demonstrate that the principlesdisclosed herein are applicable to a wide variety of different actuatorconfigurations.

In FIG. 2, the actuator 14 includes a piston member 54 sealingly andreciprocably disposed in a generally cylindrical housing 56. The rodmember 50 is connected to the piston member 54 and extends downwardlythrough a lower end of the housing 56.

The power source 12 in this example comprises a hydraulic pressuresource (such as, a hydraulic pump and associated equipment) forsupplying energy in the form of fluid pressure to a chamber 58 in thehousing 56 below the piston member 54. To raise the piston member 54,the rod member 50 and the rod string 18, hydraulic fluid at increasedpressure is supplied to the chamber 58 from the power source 12. Tocause the piston member 54, rod member 50 and rod string 18 to descend,the pressure in the chamber 58 is reduced (with hydraulic fluid beingreturned from the chamber to the power source 12).

In this example, the sensor 52 is attached externally to the housing 56.In other examples, the sensor 52 could be positioned internal to, or ina wall of, the housing 56. The scope of this disclosure is not limitedto any particular position or orientation of the sensor 52.

A magnet 60 is attached to, and displaces with, the piston member 54. Aposition of the magnet 60 (and, thus, of the piston member 54) iscontinuously sensed by the sensor 52 during reciprocating displacementof the piston member. A suitable magnet for use in the actuator 14 is aneodymium magnet (such as, a neodymium-iron-boron magnet) in ring form.However, other types and shapes of magnets may be used in keeping withthe principles of this disclosure.

A suitable linear position sensor (or linear variable displacementtransducer) for use as the sensor 52 in the system 10 is available fromRota Engineering Ltd. of Manchester, United Kingdom. Other suitableposition sensors are available from Hans Turck GmbH & Co. KG of Germany,and from Balluff GmbH of Germany. However, the scope of this disclosureis not limited to use of any particular sensor with the system 10.

In the FIG. 3 example, the sensor 52 is not mounted external to thehousing 56, but is instead positioned internal to another housing 62 ata lower end of the actuator 14. In this manner, the sensor 52 does nothave to detect the position of the magnet 60 through a wall of thehousing 62, and can be in closer proximity to the magnet.

In addition, the magnet 60 in the FIG. 3 example is mounted to the rodmember 50, instead of to the piston member 54. Thus, the position of anyreciprocating member of the actuator 14 can be continuously detectedusing an appropriately configured sensor 52. Note that the actuator 14in the FIG. 3 example is not necessarily a hydraulic actuator.

In the FIG. 4 example, the actuator 14 comprises a cable, ribbon, tape,belt or other flexible member 64 stored on a spool 66. The flexiblemember 64 extends upwardly about a sheave member 68 and downwardly to aconnection with the rod member 50.

The spool 66 is driven by an electric motor 70 of the power source 12,so that the flexible member 64 is alternately wound and unwound aboutthe spool, to thereby alternately raise and lower the rod member 50. Inthis example, the power source 12 and the actuator 14 may beconveniently combined, with the control system 46 controlling operationof the motor 70 to achieve a desired reciprocating displacement of therod member 50 and rod string 18 connected thereto (see FIG. 1).

The sensor 52 in the FIG. 4 example comprises a rotary encoder capableof continuously detecting a rotational position of the sheave member 68.In this manner, the position, velocity and acceleration of the sheavemember 68, the flexible member 64 and the rod member 50 (and the upperend of the rod string 18) can be continuously known.

The FIG. 5 example is similar in some respects to the FIG. 4 example,but the actuator 14 in the FIG. 5 example comprises a hydraulic cylinder72 for alternately raising and lowering the sheave member 68 to therebyalternately raise and lower the rod member 50. Similar to the FIG. 2example, the FIG. 5 power source 12 comprises a hydraulic pressuresource to alternately increase and decrease fluid pressure applied tothe cylinder 72.

The sensor 52 in the FIG. 5 example can comprise an infrared orultrasonic sensor for sensing the position of the sheave member 68 as itreciprocates upward and downward. Alternatively, the sensor 52 couldsense the position of another member of the actuator 14 as itreciprocably displaces.

Referring additionally now to FIGS. 6-9, examples of velocity profiles74 that may be used with the system 10 and method are representativelyillustrated as graphs of velocity versus position. The velocity profiles74 may be used with other systems and methods, in keeping with the scopeof this disclosure.

Since the position of a reciprocating member of the actuator 14 (or anupper end of the rod string 18) can be detected at any point in thedisplacement of the member, the control system 46 can readily determinethe velocity of the member at any point in the displacement of themember (velocity equals the derivative of position over time). Thisdetermination of velocity may be made by the control system 46, or insome examples the sensor 52 may provide an output of instantaneousvelocity, as well as position. In other examples, acceleration (equal tothe derivative of velocity over time) may also be determined by thecontrol system 46, or may be provided as an output of the sensor 52.

In the FIG. 6 example, an upstroke begins at zero velocity and at alower stroke extent 76. The velocity rapidly increases, and then levelsoff once the rod string 18 is displacing upward at a desired rate. Notethat the entire rod string 18 does not displace as an infinitely rigidmember. Instead, the rod string 18 has some elasticity and there aredampening effects present (such as, friction between the rod string 18and the tubing string 30, etc.), so that the reciprocating displacementof a lower end of the rod string at the downhole pump 20 is not the sameas the reciprocating displacement of the upper end of the rod string atthe surface.

Accordingly, a wave equation in the rod string 18 can be solved, so thatthe velocity profile 74 to be maintained at the surface corresponds to adesired velocity profile at the downhole pump 20. The Everitt-Jenningsalgorithm may be used to solve the wave equation (see Everitt, T. A. andJennings, J. W., An Improved Finite-Difference Calculation of DownholeDynamometer Cards for Sucker-Rod Pumps, SPE 18189, February 1992).Although the full Everitt-Jennings algorithm produces a calculation ofload versus position, the algorithm can be used to calculate velocity(and acceleration) as an intermediate step.

Thus, working “backward” from a desired velocity profile at the downholepump 20, solution of the wave equation produces a corresponding desiredvelocity profile at the surface (e.g., at a reciprocating member of theactuator 14, or an upper end of the rod string 18). The desired velocityprofile (either the desired velocity profile at the surface, or thedesired velocity profile at the downhole pump 20 if the wave equation isto be solved by the control system 46) may be input to the controlsystem, and the control system can then operate the power source 12 andthe actuator 14, so that any deviation of the velocity profile asdetected by the sensor 52 from the desired velocity profile isminimized.

Referring again to the velocity profile 74 of FIG. 6, it will beappreciated that, when the velocity increases rapidly from the lowerstroke extent 76, the upper end of the rod string 18 will begindisplacing before the lower end of the rod string. Thus, the rapidvelocity increase can be used to obtain displacement of the lower end ofthe rod string 18 relatively quickly, and then the velocity can leveloff once the entire rod string is displacing.

Near an end of the upstroke, the velocity rapidly decreases to zerovelocity at the upper stroke extent 78. Note that there is desirably aslope to the profile 74 prior to the upper stoke extent 78, instead ofan abrupt reversal of direction, which would be inefficient and possiblydamaging to system components. Similarly, although the profile 74 isdepicted as being composed of straight line segments, in practice theprofile would have smoother transitions.

The downstroke in the FIG. 6 example is a mirror image of the upstroke.However, it is not necessary for this to be the case and, as discussedmore fully below, it can be beneficial for there to be differences inthe velocity profile 74 between the upstroke and the downstroke.

In the FIG. 7 example, a slope of the velocity profile 74 changesmultiple times on the upstroke after the lower stroke extent 76 andprior to the upper stroke extent 78. The downstroke is again a mirrorimage of the upstroke, and so the velocity profile slope changesmultiple times on the downstroke after the upper stroke extent 78 andprior to the lower stroke extent 76.

Such changes in the velocity profile 74 may be used to account for thefact that progressively more of the rod string 20 is being displacedover time after the upper and lower stroke extents 78, 76, and thatprogressively more of the rod string is being slowed to zero velocityprior to the upper and lower stroke extents.

In the FIG. 8 example, the downstroke is a reversed mirror image of theupstroke, with multiple velocity profile slope changes after each of thelower and upper stroke extents 76, 78, and with a single velocity slopechange prior to each of the lower and upper stroke extents. This exampledemonstrates that a wide variety of different shapes are possible forthe velocity profile 74.

In the FIG. 9 example, a maximum velocity (absolute value) on thedownstroke is much less than a maximum velocity on the upstroke. Thisvelocity profile 74 can be beneficial in avoiding a gas-lock condition,since the reduced downstroke velocity can provide more time for thedownhole pump 20 to fill, as well as provide more precise control overthe lower stroke extent at the downhole pump (momentum effects on thedownward moving rod string 18 are more controllable and predictable, ascompared to the upstroke). In other examples, a reduced velocity may beprovided on the upstroke to reduce stresses in the rod string 18. Thus,the scope of this disclosure is not limited to any particular velocityprofile, or to any particular relationship between upstroke anddownstroke velocity profiles.

Since the control system 46 knows the velocity at any point duringreciprocating displacement (the velocity being provided by thecontinuous position sensor 52 output, or being calculated by the controlsystem based on the sensor output), the control system can at any pointduring the reciprocating displacement compare the detected velocity tothe desired velocity, and vary operation of the power source 12 and theactuator 14 as needed to minimize any discrepancies. In this manner, thecontrol system 46 can maintain a preselected desired velocity profile ata member of the actuator 14, the rod string 18 at the surface, and therod string at the downhole pump 20.

In addition, the velocity profile 74 can be changed as needed to achieveother objectives. For example, if it is desired to change the positionof the lower and/or upper stroke extents 76, 78, the velocity profile 74can be appropriately changed, and the control system 46 will accordinglychange its operation of the power source 12 and the actuator 14.Similarly, the velocity profile 74 can be changed, if desired, toachieve increased efficiency, increased production, reduced rod stringwear, increased rod string usable life, reduced electricity consumptionor peak load, or in response to changed conditions (such as, depletionof a reservoir, pump-off, pump-pound, gas-lock, etc.).

Referring additionally now to FIGS. 10 & 11, an example technique ormethod 80 for controlling operation of the well pumping system 10 isrepresentatively illustrated in flowchart form. In this method 80, it isdesired to change one or both of the lower and upper stroke extents 76,78 at the surface, in order to achieve a corresponding (although notnecessarily equal) change in stroke extent(s) of the rod string 18 atthe downhole pump 20.

Similar methods or techniques may be used to achieve other changes inthe reciprocating displacement of the rod string 18 at the downhole pump20. For example, similar methods may be used to change velocity,acceleration or stroke length of the rod string 18 at the downhole pump20. Thus, the scope of this disclosure is not limited to any particularchange made in the reciprocating displacement of the rod string 18.

In step 82 of the method 80, the stroke extents 76, 78 are detected atthe surface (for example, using the continuous position sensor 52). Thestroke extents 76, 78 in this example correspond to minimum and maximumdisplacement values detected by the sensor 52, and to positions at whichthe velocity is zero.

The continuous position sensor 52 may detect the position of a member ofthe actuator 14 (such as, the rod member 50, the piston member 54, thesheave member 68 or another member), or the upper end of the rod string18 (for example, by positioning the sensor 52 in or on the stuffing box44). The scope of this disclosure is not limited to the position of anyparticular component being detected by the continuous position sensor52.

In step 84, a desired change to one or both of the stroke extents 76, 78is determined. For example, it may be desired to increase a strokedistance by changing one or both of the stroke extents 76, 78, in orderto increase the pumping rate. As another example, it may be desired toraise the lower stroke extent at the downhole pump 20, in order toalleviate a pump-pound condition. As yet another example, it may bedesired to change one or both of the stroke extents at the downhole pump20, in order to increase a work output of the system 10.

The determination of the desired change to one or both of the strokeextents 76, 78 may be made automatically by the control system 46 (forexample, in response to detection of a pump-pound condition, detectionof a pump-off condition, detection of a reduction in work output, etc.),or as part of a pre-programmed routine (for example, to periodicallyadjust the lower stroke extent, so that maximum compression is achievedon the downstroke to avoid gas-lock). Alternatively, the determinationmay be made elsewhere and then input to the control system 46 by a user.

In step 86, the control system 46 modifies the operation of the powersource 12 and actuator 14 as needed to achieve the desired change. Sincethe continuous position sensor 52 provides to the control system 46 acontinuous output of position during the reciprocating displacement inthis example, the control system can make any appropriate changes inoperation while the reciprocating displacement continues, and withoutany need to change the sensor's position relative to the actuator 14 orany other component of the system 10.

The control system 46 can change operation of the power source 12 andactuator 14, for example, by varying a duration, level, relative timing,frequency, etc., of energy supplied to the actuator from the powersupply 12. An example is described more fully below in relation to thegraph illustrated in FIG. 12.

In FIG. 11, the step 84 of determining the desired change to the strokeextent(s) at the surface is more particularly expanded for a situationwhere it is desired to increase a work output at the downhole pump 20.For example, work output at the downhole pump 20 may be monitored overtime, and a decrease in work output can be indicative of a pump-poundcondition. Thus, if a decrease in work output at the downhole pump 20 isdetected, the method 80 can be used to change the stroke extent(s) asneeded to alleviate the pump-pound condition and thereby increase thework output.

As mentioned above, the Elliott-Jennings algorithm may be used to solvethe wave equation in the rod string 18 and determine load (force) versusposition (displacement) at the downhole pump 20. Since work equals forceapplied over a distance, a force versus displacement curve at thedownhole pump 20 (also known to those skilled in the art as a “downholecard”) can be integrated to determine work output.

In one technique, the lower stroke extent of the rod string 18 at thedownhole pump 20 can be incrementally raised by the control system 46 tothereby alleviate the pump-pound condition and increase the work output.Steps 88-92 can be repeated for each increment, until the work output issufficiently increased.

For example, the control system 46 can monitor the work output in step88. In step 90, a desired change in the lower stroke extent (the amountof the incremental raising) at the downhole pump 20 is determined. Thisdesired change in the lower stroke extent at the downhole pump 20 may bedetermined separately for each occurrence of a pump-pound condition, orit may be preselected (for example, by user input or initial programmingof the control system 46).

In step 92, a desired change in the lower stroke extent at the surfacecorresponding to the desired change in the lower stroke extent at thedownhole pump 20 is determined. Again, the solution to the wave equationin the rod string 18 can be used to relate reciprocating displacement atthe downhole pump 20 to reciprocating displacement at the surface (forexample, using the Elliott-Jennings algorithm or another suitablealgorithm), in order to determine the desired change in the lower strokeextent at the surface.

The control system 46 can then modify operation of the power source 12and actuator 14 as needed to achieve the desired change (as in step 86).The continuous position sensor 52 output will confirm whether themodified operation in fact achieves the desired change, and the controlsystem 46 will make further modifications as needed to minimize anydiscrepancies between the detected change and the desired change inlower stroke extent at the surface.

Referring additionally now to FIG. 12, an example graph of position andenergy input versus time is representatively illustrated. The graphdemonstrates how characteristics of the reciprocating displacement canbe varied by modifying the energy input to the actuator 14 from thepower source 12.

As discussed above, the control system 46 can control the energy inputto the actuator 14 to achieve various objectives. In the FIG. 12example, an upper stroke extent (e.g., of an actuator member, or the rodstring 18 at the surface or at the downhole pump) is desired to beraised, and two different ways of achieving this objective are depictedin FIG. 12.

In a solid line, the position (for example, as detected by thecontinuous position sensor 52 and optionally resulting from a solutionof the wave equation in the rod string 18) is depicted over time priorto modification of the energy input to the actuator 14. The energy inputover time is also depicted as a solid line prior to modification.

Note that the upper stroke extent 78 occurs after the energy inputperiodically decreases to a minimum level, and the lower stroke extent76 occurs after the energy input periodically increases to a maximumlevel. This is due to inertia and friction effects on the rod string 18,so that the rod string does not immediately begin to displace upwardwhen the energy input is increased, and the rod string does notimmediately begin to displace downward when the energy input isdecreased.

One technique of raising the upper stroke extent 78 is depicted inrelatively long dashed lines in FIG. 12. In this technique, a durationof the maximum energy input level is increased, so that the rod string18 displaces upward over a correspondingly increased duration. Since therod string 18 displaces upward longer, the upper stroke extent 78 israised.

Another technique of raising the upper stroke extent 78 is depicted inrelatively short dashed lines in FIG. 12. In this technique, the maximumenergy input level is increased, so that the acceleration and velocityof the rod string 18 on the upstroke is correspondingly increased. Sincethe rod string 18 displaces faster upward, the upper stroke extent 78 israised.

The example of FIG. 12 demonstrates that a variety of differenttechniques and combinations of techniques may be used by the controlsystem 46 to modify the reciprocating displacement characteristics ofthe rod string 18. Such techniques may be used to modify the velocity(including upstroke and downstroke velocity profiles), acceleration(including upstroke and downstroke acceleration profiles), lower andupper stroke extents, and stroke length of the rod string 18 at surfaceand at the downhole pump 20.

As mentioned above, use of the continuous position sensor 52 with thesystem 10 is not necessary. In further examples described below, othermethods of determining the position of a member of the actuator 14 or anupper end of the rod string 18 are provided. However, it should beclearly understood that the scope of this disclosure is not limited toany particular method or technique for determining position,displacement, velocity, acceleration or any other characteristic ofreciprocating motion.

Referring additionally now to FIG. 13, another example of the actuator14 in the well pumping system 10 and associated method isrepresentatively illustrated. The FIG. 13 example is similar in mostrespects to the FIG. 2 example, but the continuous position sensor 52 isnot used in the FIG. 13 example. However, the continuous position sensor52 could be used with the FIG. 13 example in keeping with the principlesof this disclosure.

As depicted in FIG. 13, a discrete position sensor 100 is used to detectwhen the magnet 60 (and, thus, the piston member 54 or anotherreciprocating member of the actuator 14, or the upper end of the rodstring 18) is at a particular position. The sensor 100 is shown as beingdisposed between the upper and lower stroke extents of the piston 54,but in other examples, the sensor 100 could be located at or near theupper or lower stroke extent.

Only a single sensor 100 is depicted in FIG. 13. However, in otherexamples, other numbers of sensors may be used. For example, a sensor100 could be located at or near the upper stroke extent, and anothersensor 100 could be located at or near the lower stroke extent. Thescope of this disclosure is not limited to use of any particular numberor location of sensors in or on the actuator 14.

A suitable magnetic field sensor for use as the sensor 100 is a PepperIMB-F32-A2 magnetic flux sensing switch marketed by PepperI+Fuchs NorthAmerica of Twinsburg, Ohio USA. However, other magnetic field sensors orother types of discrete position sensors may be used in keeping with theprinciples of this disclosure.

The sensor 10 is used in conjunction with a flowmeter 102 in the FIG. 13example to continuously determine the position of the piston member 54(or another reciprocating member of the actuator 14, or the upper end ofthe rod string 18). The flowmeter 102 measures flow of fluid between thepower source 12 and the actuator 14.

The flowmeter 102 may be a volumetric or mass flowmeter. In thisexample, the flowmeter 102 is a positive displacement volumetricflowmeter.

However, other types of flow measurements may be made by the flowmeter102 in keeping with the scope of this disclosure.

Assuming that the fluid displaced into and out of the chamber 58 isincompressible and there is no fluid leakage, a certain fluid volumewill correspond to a certain displacement of the piston member 54(displacement equals fluid volume divided by piston area). If a massflowmeter is used, the fluid volume can be determined from the densityof the fluid (volume equals mass divided by density).

Combined with the position sensing provided by the sensor 100, theposition of the piston member 54 at every point in its reciprocatingdisplacement can be readily determined (current position equals previousposition plus displacement). The sensor 100 can also be used forcalibration of the flowmeter 102, for example, to compensate forcompressibility of the fluid, leakage of fluid, etc.

Thus, using the sensor 100 and flowmeter 102, the position,displacement, velocity (derivative of displacement over time) andacceleration (derivative of velocity over time) of the piston member 54can be known continuously during the reciprocation of the rod string 18.The control system 46 can use this information as described above tocontrol the reciprocating displacement of the rod string 18.

If the assumption that the fluid is incompressible results in anunacceptable level of inaccuracy in calculating and controlling thereciprocating displacement, additional sensors may be used to improveaccuracy. For example, a pressure sensor 104 can be used to monitorpressure in the chamber 58, so that compressibility of the fluid can becompensated for in the displacement calculation. A temperature sensor106 can also be used to monitor the temperature of the fluid, forexample, in the event that a gas is entrained in the fluid (so that itsvolume changes substantially in response to temperature changes), or thefluid is of a type (such as silicone-based hydraulic fluid) that has arelatively high coefficient of thermal expansion. If a mass flowmeter isused for the flowmeter 102, it will be appreciated that volumecalculations will be aided by the temperature measurements provided bythe temperature sensor 106 (since for most fluids density changes inresponse to temperature changes).

Referring additionally now to FIG. 14, another example of the actuator14 in the system 10 is representatively illustrated. The FIG. 14 exampleis similar in most respects to the example of FIG. 3, but in the FIG. 14example multiple discrete position sensors 100 are used in place of thecontinuous position sensor 52, and the flowmeter 102, pressure sensor104 and temperature sensor 106 are used for improved accuracy.

As depicted in FIG. 14, one of the position sensors 100 is located at ornear each of the upper and lower stroke extents of the magnet 60. Bydetecting arrival of the magnet 60 at multiple relatively widely spacedapart locations, position calculations based on measurements made by theflowmeter 102 (with or without use of the other sensors 104, 106) aremore readily calibrated. For example, it will be appreciated that thepiston area of the piston member 54 multiplied by the known distancebetween the sensors 100 equals the change in volume of the chamber 58.If the change in volume calculated based on the flowmeter 102measurements does not equal the change in volume detected based on theoutput of the sensors 100, an appropriate calibration coefficient can beapplied as needed.

Another type of discrete position sensor that may be used for thesensors 100 in the FIG. 14 example is a photoelectric sensor. In thatcase, an optically discernible member (such as, a member having a color,texture, refractive index or other optical characteristic different fromthe surrounding environment) could be used in place of the magnet 60.The scope of this disclosure is not limited to use of any particulartype of sensor, or to any particular technique for detecting 2 0position.

Although two position sensors 100 are depicted in FIG. 14, any number ofsensors may be used in keeping with the principles of this disclosure.Although the sensors 100 are described above as being located at or nearthe upper and lower stroke extents of the magnet 60, the sensors may beotherwise located. Thus, the scope of this disclosure is not limited toany of the details of the sensor(s) 100 placement, quantity,configuration or arrangement as depicted in FIGS. 13 & 14, or asdescribed above.

Note that any of the sensors 52, 100, 102, 104, 106 described above maybe used alone or in combination with any of the other sensors. Forexample, the flowmeter 102 could be used alone to determine theposition, displacement, velocity and acceleration of a member of theactuator 14 (or the upper end of the rod string 18) with acceptableaccuracy in some situations. One discrete position sensor 100 wouldprovide for convenient initialization and calibration of thedisplacement determinations, and multiple sensors 100 provide forenhanced accuracy, but use of these sensors is not necessary in keepingwith the principles of this disclosure.

It may now be fully appreciated that the above disclosure providessignificant advancements to the arts of monitoring and controllingoperation of a well pumping system. In examples described above, thewell pumping system 10 can be precisely controlled, in part by utilizingthe continuous position sensor 52 to provide substantially continuousoutput of position to the control system 46 as the actuator 14reciprocates the rod string 18. In other examples, the flowmeter 102,discrete position sensor(s) 100 and/or other sensors 104, 106 may beused instead of, or in addition to, the continuous position sensor 52for determining displacement of a member of the actuator 14 or an upperend of the rod string 18.

The above disclosure provides to the art a well pumping system 10. Inone example, the system 10 can include an actuator 14 that reciprocablydisplaces a rod string 18, a flowmeter 102 that measures flow of a fluidbetween a power source 12 and the actuator 14, and a control system 46that modifies reciprocal displacement of the rod string 18 by theactuator 14, in response to an output of the flowmeter 102.

The well pumping system 10 can also include at least one discreteposition sensor 100 that detects when a member (e.g., rod member 50,piston member 54, magnet 60) of the actuator 14 or an upper end of therod string 18 is at a predetermined position.

The control system 46 may modify a stroke extent of a member (e.g., rodmember 50, piston member 54, magnet 60) of the actuator 14, or a strokeextent of the rod string 18 at surface or proximate a downhole pump 20,in response to the output of the flowmeter 102.

The control system 46 may maintain a preselected velocity profile 74 ofa member of the actuator 14, or of the rod string 18 at surface or at adownhole pump 20, in response to the output of the flowmeter.

A well pumping method 80 is also provided to the art by the abovedisclosure. In one example, the method 80 can include reciprocablydisplacing a rod string 18, continuously determining a velocity profile74 of the rod string 18, and modifying the velocity profile 74 while therod string 18 reciprocably displaces, in response to an output of aflowmeter 102.

The modifying step can comprise changing a duration of the velocityprofile 74. The changing may be performed while the rod string 18reciprocably displaces.

The modifying step can comprise changing a position at which an actuatormember velocity is zero, the position being detected based on the outputof the flowmeter 102. The changing may be performed while the rod string18 reciprocably displaces.

The modifying step may comprise changing a position at which the rodstring 18 velocity is zero at a downhole pump 20. The changing cancomprise solving a wave equation in the rod string 18.

The modifying step may comprise minimizing differences between thedetected velocity profile and a preselected velocity profile. Themodifying step may comprise maintaining acceleration of the rod string18 less than a preselected level.

Another well pumping method is disclosed above. In this example, themethod comprises reciprocably displacing a rod string 18 with anactuator 14, continuously determining displacement in response to anoutput of a flowmeter 102, and modifying reciprocating displacement ofthe rod string 18 by the actuator 14, in response to the output of theflowmeter 102.

The determined displacement may be calibrated in response to an outputof at least one discrete position sensor 100.

The modifying step may comprise varying a periodic energy input to theactuator 14 relative to the reciprocating displacement of the rod string18. The varying can comprise varying a duration of the energy inputand/or varying a level of the energy input.

The modifying step may comprise varying a stroke extent. The varying caninclude displacing the stroke extent until either: a) the stroke extentis positioned at a preselected stroke extent, or b) the stroke extenthas displaced a preselected distance.

Although various examples have been described above, with each examplehaving certain features, it should be understood that it is notnecessary for a particular feature of one example to be used exclusivelywith that example. Instead, any of the features described above and/ordepicted in the drawings can be combined with any of the examples, inaddition to or in substitution for any of the other features of thoseexamples. One example's features are not mutually exclusive to anotherexample's features. Instead, the scope of this disclosure encompassesany combination of any of the features.

Although each example described above includes a certain combination offeatures, it should be understood that it is not necessary for allfeatures of an example to be used. Instead, any of the featuresdescribed above can be used, without any other particular feature orfeatures also being used.

It should be understood that the various embodiments described hereinmay be utilized in various orientations, such as inclined, inverted,horizontal, vertical, etc., and in various configurations, withoutdeparting from the principles of this disclosure. The embodiments aredescribed merely as examples of useful applications of the principles ofthe disclosure, which is not limited to any specific details of theseembodiments.

In the above description of the representative examples, directionalterms (such as “above,” “below,” “upper,” “lower,” “raised,” “lowered,”etc.) are used for convenience in referring to the accompanyingdrawings. However, it should be clearly understood that the scope ofthis disclosure is not limited to any particular directions describedherein.

The terms “including,” “includes,” “comprising,” “comprises,” andsimilar terms are used in a non-limiting sense in this specification.For example, if a system, method, apparatus, device, etc., is describedas “including” a certain feature or element, the system, method,apparatus, device, etc., can include that feature or element, and canalso include other features or elements. Similarly, the term “comprises”is considered to mean “comprises, but is not limited to.”

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments ofthe disclosure, readily appreciate that many modifications, additions,substitutions, deletions, and other changes may be made to the specificembodiments, and such changes are contemplated by the principles of thisdisclosure. For example, structures disclosed as being separately formedcan, in other examples, be integrally formed and vice versa.Accordingly, the foregoing detailed description is to be clearlyunderstood as being given by way of illustration and example only, thespirit and scope of the invention being limited solely by the appendedclaims and their equivalents.

What is claimed is:
 1. A well pumping system, comprising: an actuatorthat reciprocably displaces a rod string; a flowmeter that measures flowof a fluid between a power source and the actuator; and a control systemthat modifies reciprocal displacement of the rod string by the actuator,in response to an output of the flowmeter.
 2. The well pumping system ofclaim 1, further comprising at least one discrete position sensor thatdetects when a member of the actuator or an upper end of the rod stringis at a predetermined position.
 3. The well pumping system of claim 1,wherein the control system modifies a stroke extent of a member of theactuator, in response to the output of the flowmeter.
 4. The wellpumping system of claim 1, wherein the control system modifies a strokeextent of the rod string at surface, in response to the output of theflowmeter.
 5. The well pumping system of claim 1, wherein the controlsystem modifies a stroke extent of the rod string proximate a downholepump, in response to the output of the flowmeter.
 6. The well pumpingsystem of claim 1, wherein the control system maintains a preselectedvelocity profile of a member of the actuator, in response to the outputof the flowmeter.
 7. The well pumping system of claim 1, wherein thecontrol system maintains a preselected velocity profile of the rodstring at surface, in response to the output of the flowmeter.
 8. Thewell pumping system of claim 1, wherein the control system maintains apreselected velocity profile of the rod string proximate a downholepump, in response to the output of the flowmeter.
 9. A well pumpingmethod, comprising: reciprocably displacing a rod string; continuouslydetermining a velocity profile of the rod string; and modifying thevelocity profile while the rod string reciprocably displaces, inresponse to an output of a flowmeter.
 10. The well pumping method ofclaim 9, wherein the modifying comprises changing a duration of thevelocity profile.
 11. The well pumping method of claim 10, wherein thechanging is performed while the rod string reciprocably displaces. 12.The well pumping method of claim 9, wherein the modifying compriseschanging a position at which an actuator member velocity is zero, theposition being determined based on the output of the flowmeter.
 13. Thewell pumping method of claim 12, wherein the changing is performed whilethe rod string reciprocably displaces.
 14. The well pumping method ofclaim 9, wherein the modifying comprises changing a position at whichthe rod string velocity is zero at a downhole pump.
 15. The well pumpingmethod of claim 14, wherein the changing comprises solving a waveequation in the rod string.
 16. The well pumping method of claim 9,wherein the modifying comprises minimizing differences between thedetected velocity profile and a preselected velocity profile.
 17. Thewell pumping method of claim 9, wherein the modifying comprisesmaintaining acceleration of the rod string less than a preselectedlevel.
 18. A well pumping method, comprising: reciprocably displacing arod string with an actuator; continuously determining displacement inresponse to an output of a flowmeter; and modifying reciprocatingdisplacement of the rod string by the actuator, in response to theoutput of the flowmeter.
 19. The well pumping method of claim 18,wherein the determined displacement is calibrated in response to anoutput of at least one discrete position sensor.
 20. The well pumpingmethod of claim 18, wherein the modifying comprises varying a periodicenergy input to the actuator relative to the reciprocating displacementof the rod string.
 21. The well pumping method of claim 20, wherein thevarying comprises varying a duration of the energy input.
 22. The wellpumping method of claim 20, wherein the varying comprises varying alevel of the energy input.
 23. The well pumping method of claim 18,wherein the modifying comprises varying a stroke extent.
 24. The wellpumping method of claim 23, wherein the varying comprises displacing thestroke extent until either: a) the stroke extent is positioned at apreselected stroke extent, or b) the stroke extent has displaced apreselected distance.
 25. The well pumping method of claim 18, whereinthe modifying comprises modifying a stroke extent of the rod string atsurface.
 26. The well pumping method of claim 18, wherein the modifyingcomprises modifying a stroke extent of the rod string proximate adownhole pump.
 27. The well pumping method of claim 26, whereinmodifying the stroke extent of the rod string proximate the downholepump comprises solving a wave equation in the rod string.
 28. The wellpumping method of claim 18, wherein the modifying comprises maintaininga preselected velocity profile of a member of the actuator.
 29. The wellpumping method of claim 18, wherein the modifying comprises maintaininga preselected velocity profile of the rod string at surface.
 30. Thewell pumping method of claim 18, wherein the modifying comprisesmaintaining a preselected velocity profile of the rod string proximate adownhole pump.
 31. The well pumping method of claim 30, whereinmaintaining the preselected velocity profile of the rod string proximatethe downhole pump comprises solving a wave equation in the rod string.32. The well pumping method of claim 18, wherein the modifying comprisesmaintaining a preselected velocity profile, during the reciprocatingdisplacement of the rod string.